1. Field of the Invention
This invention relates to an attribute filter for computer graphics applications and, more particularly, to a method and apparatus for filtering PHIGS attributes such as detectability, highlighting and invisibility.
2. Description of the Related Art
Programmer's Hierarchical Interactive Graphics System (PHIGS) is an applications programming interface (API) widely used in computer graphics applications. PHIGS primitives have various attributes, including the attributes of detectability (or pickability), highlighting, and visibility. Highlighting indicates whether the images of subsequent output primitives encountered during structure traversal are to be distinguished in a workstation-dependent manner. Visibility indicates whether output primitives are rasterized for display. Detectability (or pickability) indicates whether a primitive is eligible for a user selection operation known as picking.
Graphics applications written to the PHIGS standard use the filter operations to control detectability, highlighting and invisibility of such primitives as lines, surfaces, text and markers. A discussion of PHIGS filters may be found in the IBM publication The graPHIGS.TM. Programming Interface: Understanding Concepts, SC33-8102-2, pp. 6-9 to 6-10 (3d ed. 1988), as well as in Hempel et al. U.S. Pat. No. 4,870,599, entitled "Traversal Method for a Graphics Display System". (IBM and graPHIGS are trademarks of IBM Corporation.) Large applications may invoke filter operations with such frequency that the filter operation processing time becomes a major factor in the overall performance of a graphics processor.